What was the carrier aircraft for the X 37 test drops at EAFB circa 2005/6 ?
I know Mf and I can calculate V, but how do I calculate Ts?! I can't find any formula for it!
Unless of course, someone happens to have some past data on the L* of 100-200N class H202/RP-1 engines.
Quote from: CitizenSpace on 05/16/2015 08:48 amI know Mf and I can calculate V, but how do I calculate Ts?! I can't find any formula for it! Because there is no neat compact formula for it. Ts is the answer to the question how long does it take for the propellants to properly combust. To mathematically find that out you have to model propellant injection, mixing, atomization and combustion. Things like injector droplet size, droplet vaporization rate and turbulence matter. The choice of propellants is most prominent factor so past experience gets you to the right ballpark.QuoteUnless of course, someone happens to have some past data on the L* of 100-200N class H202/RP-1 engines. Huzel'n'Huang to the rescue.Page 87. HTP/RP-1 L* 60-70 inches including the catalyst bed.
Also about the formula, is 'no neat and compact formula for it' mean there can't be on, because of incredibly-hard to model-mathematically variables? Or is it just because it would be very difficult to make one and no can really be bothered when we have past experience at hand.
Also, 1.5m seems a bit long for a 100N engine...
Quote from: CitizenSpace on 05/17/2015 07:57 amAlso, 1.5m seems a bit long for a 100N engine...Note that even though it looks like 'length' it is really just another form to express the stay time. The propellants don't know nor care whether they go into 100N engine or 1000,000N engine, the proper mixing and combustion takes about the same time in both cases.Smaller engines tend to have higher combustion chamber contraction ratio than larger engines in order to achieve required L* without being impracticaly long.
Ah! Thanks, kraisee. That makes sense.This actually brings up a point I haven't heard the SSTO folks talk about. Using conventional technology, even if one was willing to accept the abysmal payload payload capability, the associated accelerations near the end of it's burn would be extreme unless the propulsion system consisted of numerous identical engines, most of which would get shut down throughout its flight, or incorporate smaller sustainer engines. Having just a few [large] engines would not be possible, assuming a practical lower limit for throttlability. Does that sound right?
Having just a few [large] engines would not be possible, assuming a practical lower limit for throttlability. Does that sound right?
And what talking about does not apply for launch vehicles leaving Mars or the Moon- for number reasons- main reason is roughly need 9 rocket fuel to lift 1 payload from Earth. The Moon 1 rocket fuel to 1 payload, and Mars about 2 rocket fuel to 1 payload. Another reason is the low gravity loss for Moon and Mars.
The 3g figure was for stated 40% Mvac throttle. But kraisee is right, they probably floor it all the way up.Quote from: msat on 07/10/2015 04:32 pm Having just a few [large] engines would not be possible, assuming a practical lower limit for throttlability. Does that sound right?You need to define the practical lower limit. LEM descent engine demonstrated 10% throttle using moving pintle. YouKnowWhoX is already using pintle injector, adding a moving sleeve to increase throttleability (is that a word?) wouldn't be a huge step.Another question is would you need to use the engines for landing too. In that case just a few large ones are problematic.
Merlin is a pintle engine. Cheers, Martin
Quote from: MP99 on 07/12/2015 10:05 amMerlin is a pintle engine. Cheers, MartinYeah, I was aware of that, but R7 made it sound like it's fixed position, so throttling is accomplished by other means.